After Sep. 11, 2001, letters contaminated with weapons-grade Bacillus anthracis (anthrax) spores passed through the United States Postal Service (USPS). Over 16 cases of documented infections and several deaths were directly attributed to such letters. By November 2001, over 32,000 individuals in the United States were taking antibiotics prescribed by physicians specifically as a prophylactic measure to combat a potential exposure to anthrax contaminated mail. Multiple mail processing facilities, and the equipment within those facilities, were contaminated by exposure to what appears to have been a statistically small number of intentionally contaminated letters.
In response to the threat posed by intentionally contaminated mail, most of the incoming mail passing through most of the larger USPS mail distribution centers is now screened for anthrax. However, not all mail handled by the USPS passes through one of these distribution centers. Furthermore, the USPS mail screening system only detects Bacillus anthraces (i.e., anthrax), but currently does not attempt to detect ricin, tularemia or any of the other biological hazardous threats or “bio-threats.” Also, bulk mail such as boxes of pamphlets, and mass advertising mailings are not screened by the USPS and are often shipped by overnight carriers such as United Parcel Service (UPS), which does not screen any packages for bio-threats.
The USPS solution, which was developed by Northrop Grumman Corporation, uses a type of nucleic acid amplification and detection based on genetic fingerprinting known as polymerase chain reaction (PCR) technology. PCR uses polymerase enzymes to cause a chain reaction that results in a massive increase in the number of copies of a targeted gene sequence—but if and only if the targeted gene sequence is present in a sample being tested. For example, if a sample of paper dust extracted from an envelope in the mail does NOT contain the genes for anthrax, then the PCR test does not produce a positive result, since the gene is not present to be amplified by copying. On the other hand, if the paper dust sample contains multiple anthrax spores, the process will produce a readily detectable increase in the number of copies of the gene sequence. Thus, this detection technique normally provides a very dependable positive detection of the genes for anthrax. Other non-PCR nucleic acid amplification technologies could also be used.
In the USPS bio-threat detection scheme, samples are collected continuously, and an analysis of the samples is performed once per hour. In order to save money, the USPS decided it would only test for the anthrax genes, and not for other microbes or for the presence of other types of bio-threats such as ricin. The reasons for limiting the tests performed are understandable, since each test for each different type of harmful organism costs approximately $25-$30, and the Post Office has approximately 1300 sampling and PCR detection machines distributed throughout the United States. Each machine generates a new sample to be tested each hour, resulting in millions of tests per year and costs that will likely exceed $100 million/year. A relatively high continuing operating cost is thus one clear drawback to the USPS solution. Also, an initial capital equipment cost for the USPS sampling and detection system is on the order of $200,000 per system. For many smaller mail rooms, the initial cost of this system is thus also prohibitive.
The response time for the current USPS detection system is approximately two hours. Because of this relatively slow response time, the system only provides a “detect to treat” capability, since during the two hours before a positive detection of anthrax can occur, it can be assumed that the toxic agent will have spread throughout the mail facility. Clearly, it would be desirable to develop a system that is lower in cost to operate and which provides an immediate alert when a potential bio-threat is detected in the mail being screened. In addition, it would be desirable to screen the mail for other bio-threats besides anthrax.